Brain dysfunction is prevalent in the critically ill elderly, presenting in the acute setting as delirium or coma or in the long-term as impairment in global cognition and executive functioning. This brain dysfunction results in increased hospital cost, length of stay, functional dependence, and mortality. The pathophysiology of this brain dysfunction remains unclear but likely involves endothelial dysfunction and injury to the blood brain barrier and neurons. With the increasing age of the population and continued high morbidity from critical illness states, the acute and long-term cognitive effects of critical illnes that are unique to the elderly must be studied, and the mechanistic roles of potential pathophysiological pathways such as endothelial dysfunction and neurologic injury in this brain dysfunction of the elderly must be elucidated. The overall objectives of this research project, therefore, focus on testing the global hypothesis that systemic endothelial dysfunction and neurologic injury lead to acute brain dysfunction during critical illness and long-term cognitive impairment after in survivors. This research will provide new insights into the pathophysiology of critical illness brain dysfunction, and this grant will allow the principal investigator to delve ito these pathophysiological mechanisms while gaining experience in the unique challenges of researching brain dysfunction in the elderly. The data obtained during this grant period will lead toward more detailed mechanistic studies by the principal investigator of brain dysfunction in the elderly. Importantly, the results of this line of research may lead to future therapeutic trials of endothelial or blood brain barrier modulation designed to improve the cognitive outcomes our elderly ICU patients.